1. Field of the Invention
This invention relates generally to a heat exchanger for fluids, and more specifically, this invention relates to a cold plate heat exchanger for cooling carbonated water in a beverage dispenser.
2. Description of the Prior Art
In many locations where it is desired to dispense carbonated beverages, it is either impossible or undesirable to provide a compression-expansion refrigeration system. Examples of such locations are ball parks, circuses or carnivals, large picnic or social gatherings, and a variety of other such situations in which limited usage does not warrant the installation of a full scale mechanical refrigerating apparatus.
Carbonated beverage dispensers for such locations utilize a so-called "cold plate" heat exchanger, in which ice is located on a heat conducting medium to withdraw heat from the fluids to be cooled. The cold plate normally has tubes or coils of a suitable material, such as stainless steel, imbedded in a heat conducting casting, such as an aluminum casting. Melt water from the ice is constantly drained from the surface of the ice contacting the cold plate by a sloping depression formed in the top of the cold plate and removed by a suitable drain arrangement.
For a carbonated beverage dispenser, maximum cooling of the carbonated water is desired, since it is the major constituent of the dispensed beverage. Prior art arrangements generally use a carbonated water duct formed as a convoluted or serpentine coil located as close to the surface on which the ice is resting as is practicable. Such an arrangement has some problems. First of all, utilization of a single layer of tubing limits the amount of surface area that can be exposed to the heat exchange process. Also, the introduction of warm water close to the surface on which the ice is resting creates uneven melting of the ice and cavitation (i.e., formation of pockets or cavities so that the ice is not resting directly against the heat exchange surface). These effects limit the efficiency of the heat exchange process and can result in the dispensing of inadequately cooled beverages.
Some attempts have apparently been made to increase the cooling efficiency of the cold plate by utilizing a second layer of coiled tubing for the carbonated water. However, these prior art approaches have inserted the carbonated water to be cooled into the top layer (i.e., the layer of tubing adjacent the ice bearing surface) and then returned the carbonated water in the second layer for removal adjacent the inlet. This approach does not, of course, do anything to solve the cavitation problem. Further, by having the outlet adjacent the inlet, efficiency of the heat exchange process is reduced as a result of the cooled outlet water drawing heat from the warm inlet water.